Basic installation and adjustment guidelines for autogas systems, part I


An autogas system is a complex installation for supplying the engine with alternative fuel, such as propane-butane. The low price of fuel makes autogas very popular not only in Poland, but in the whole world. Users of cars fueled with gas gain measurable financial benefits thanks to the low operating costs of the vehicle. A high-quality, well-configured and correctly installed gas system is a source of real satisfaction. Apart from the significant financial benefits, which arise as a result of the cost of fuel being at least 50% lower than petrol prices, drivers of gas-fueled cars generate lower emissions, therefore creating less environmental damage than drivers of vehicles running on diesel or petrol. The use of propane-butane instead of petrol or diesel means that much less harmful substances are emitted. Using a car provided with a modern, properly fitted and operating autogas system is no different from using a petrol-fueled car. The performance parameters of such a vehicle, i.e. speed, horsepower and acceleration are the same as for petrol. Modern, well-mounted and properly maintained gas systems are safe for users and do not cause increased engine wear at all.

However, trouble-free operation of the gas system requires adherence to specific installation standards and adjustment procedures. In more than 80% cases, the reason for problems with the car is not related to the autogas system itself, but rather to the incorrect selection and installation of its components. Whenever a Lambda probe or engine unit fails in an engine fueled with gas, it is always an effect of installation errors.

Installation errors are sometimes the consequence of the fitter's insufficient knowledge, careless installation, trying to do things too quickly or cheaply, or even rapacity. This affects the client, the car and ultimately the fitter as well, as he has to repair his errors instead of installing systems in other cars.

Following good procedures can eliminate unnecessary errors and costs. In the following parts we will try to present specific principles for fitters that will allow them to improve the quality of services and avoid unpleasant situations in contacts with clients.

Operations performed by the fitters of autogas installtions can be divided into several key stages, i.e.:

  • inspection of the vehicle to identify any technical problems, if present,
  • acceptance of the car for gas system installation or identifying the problems which need to be dealt with to the customer,
  • if the car is accepted for installation – selection of autogas components and cost estimation,
  • external inspection of the vehicle and preparing a report for acceptance of the vehicle for installation,
  • agreement with the customer on the locations of the installed petrol/gas switch and gas filler adapter,
  • signing the report for the acceptance of the vehicle for autogas installation,
  • installation of the autogas system,
  • vehicle operating test with the gas system and necessary adjustments,
  • receipt of the car by the customer.

Vehicle diagnostics before acceptance for installation

Before autogas installation work is started, the technical condition of the vehicle must be verified. A car with engine problems will never work properly on autogas. All defects causing problems with engine operation must be repaired. Only then, can the autogas system be fitted in the car. If repairs are not carried out prior to the installation, it is more difficult to identify the cause of engine problems later. Sometimes, despite the selection of suitable components, adherence to all installation guidelines and adjustments in a test drive, the vehicle does not work well when fueled with gas. Now, the reason for this has to be found. The cause should be looked for outside the autogas system. The incorrect operation of the gas system is rather related to a defective ignition system, Lambda probe or deviating corrections of the petrol controller.

In order to avoid this, the engine should be checked for any technical problems prior to the installation, e.g. by connecting a diagnostic tester and reading the stored error codes (if present) and verifying petrol correction values or Lambda probe performance. If any sensor shows a value that deviates from the actual conditions, there will be problems with operation in the petrol fueling mode, and, as a consequence, in the gas mode. Autogas controllers partly depend on the petrol controller to determine the fuel dose.


Checks before the installation:

For installation of the autogas system in a passenger car, a key element of the procedure is to properly select all autogas components.

Selection of the autogas system

The selection of suitable components is a very important issue that is often neglected by the fitters, who are sometimes too passive and agree with the customer's suggestions too easily. It is obvious that the customer would like to pay as little as possible for the installation, and it starts with cost cutting. A cheaper system, the wrong selection of components for the specific vehicle parameters, e.g. installing a reducer recommended by the manufacturer for 90 hps to a car with a 150 hps engine. Poor quality components, poor installation services and rushing to finish the job to collect the cash. Is it worth it? Certainly not! Where is the reputation, professional service of the fitter and honorable behavior? In the long run, such an attitude, instead of profits, brings unending quarrels with unsatisfied customers, constant claims, and, as a result, the loss of customers and the reputation of the workshop.

The first important element which has to be selected to ensure performance in the entire load range, is the gas reducer. Its main task is to maintain the gas pressure in the intake part of the autogas system (reducer – injector) and change the liquid phase to the volatile phase (by adiabatic expansion), which results in a sudden drop in the temperature of the gas.

An inappropriate choice of reducer causes excessive drops in gas pressure on the inlet side when engine the load suddenly increases, which often makes the car loose power or even switch back to petrol. Sequential gas systems automatically switch to petrol when the gas pressure drops below the set limit. Thus, when the gas tank starts getting near to empty, the pressure in the whole system drops and the car is switched back to petrol. All reducers available in the market have their output specified. They are capable of "feeding" the specific horsepower installed under the bonnet. I have come across situations when a car with high horsepower had been fitted with a reducer with insufficient output, which caused problems when driving on gas. The table presents examples of reducers and their respective horsepower ranges. Manufacturers of reducers always specify the acceptable range of engine power in kW or hp in their specifications. However, theoretical values are not always equal to practical values. You should always aim for having some additional reducer output in reserve, don’t choose a reducer that is only just acceptable. It is better to play it safe and over rather than underestimate.

Another element which is important for the correct system operation is the gas injector. Currently, there are many models to choose from but every injector is different. Some of them have a very advanced design based on petrol injectors, others are very simple. In some cars, petrol is dosed in very short pulses of approx. 2 ms and some of the injectors on the market are not able to cope with it due to a design that does not allow for a fast response to the pulse sent to the coil.

The injector, just like the reducer, has its own output specified – flowrate in g/s, which concerns the ability to fill the combustion chamber sufficiently. In the primary and secondary markets, there are many 4-cylinder cars which are turbocharged and can reach the power of 300 hp. It is worth finding out how much power is covered by a single gas injector per one cylinder.

In the next part, I will discuss the selection of other elements of the autogas system and focus on the correct procedure of the handing over of the car from the customer, related risks and solutions.


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